There is a growing body of evidence that exposure to poly- and perfluoroalkyl substances (PFASs), such as perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA), adversely affect health. Water samples from private wells and public water systems collected southeast of Colorado Springs in the towns of Fountain, Widefield, and Security (FWS) detected a wide range of PFASs, including high levels of perfluorohexane sulfonate (PFHxS). It is likely that PFHxS and related compounds migrated offsite from local airfields and made their way into the public and private groundwater wells as well as into the FWS municipal water systems. The recent discovery of this contamination and the beginning of intervention efforts provides an opportunity to assess these impacts of these highly persistent PFASs at or near the peak serum levels of these compounds due to long-term exposure to high levels. We seek time-sensitive funding to characterize serum levels, explore their potential links to biomarkers of effect, and estimate the half-life in the body of PFHxS and related compounds. Our design will collect exposure information and biomarkers in participants to test the hypothesis that the FWS population exposure is associated with biomarkers of liver function, immunotoxicity, and inflammation. We will measure serum PFAS one time in 200 residents and relate this exposure to these biomarkers of effect; a second round of blood and water sampling will be used to explore persistence and the impact of intervention on drinking water levels and body burden. These biomarkers of effect were chosen based on an analysis of biologic pathways that link PFAS exposure to changes in liver function and immune effects and subsequent adverse health outcomes. By collecting baseline measurements and prospectively following 50 participants in the second year this project will develop data, tools and community networks needed to design and facilitate subsequent prospective studies that will provide insight on the health effects associated with ubiquitous PFAS exposure.